As the rate of inflation and, hence, the cost of living grows higher, the need to produce correspondingly higher earnings from one's investments grows greater, especially for persons who need, on a regular basis, a predetermined minimum income on which to live.
In calculating income levels or rates of return on one's investment, electronic calculators capable of performing annuity calculations are often used. For example, electronic calculators have been developed which are capable of performing present value (PV), future value (FV), payment (PMT), number of payments (N), and interest (I) calculations. One such device is shown and described, for example, in U.S. Pat. No. 3,863,060 entitled "General Purpose Calculator With Capacity For Performing Interdisciplinary Business Calculations," issued to France Rode, et al., Jan. 28, 1975.
However, such electronic calculators do not provide a means for calculating minimum principal amounts which could be deposited (invested) in demand accounts and in term accounts (e.g., certificate-of-deposit bank accounts which provide substantial loss of interest upon withdrawal or depletion of principal) in such a manner as to provide both a high yield and the opportunity to periodically withdraw or make payments from the deposited amounts without incurring interest penalty.
What is needed, therefore, is a convenient calculating device (e.g., a desk-top, hand-held or other portable electronic calculating device) that is capable of calculating minimum principal which could be deposited in one or more accounts with depletion-of-principal penalties so as to provide both maximum interest and penalty-free payments.